Aug. 22 project update: Bertha passes the 4,000-foot mark

Posted on Aug 22 2016 12:50 PM

Seattle Tunnel Partners crews have now mined more than 4,000 feet as they continue their push toward the SR 99 tunnel’s future north portal. As of this morning, Bertha, the SR 99 tunneling machine, had traveled approximately 4,000 feet of the 9,270-foot-long tunnel route, and installed 607 of the concrete rings that form the tunnel’s exterior walls.

The top of the cutterhead is approximately 165 feet below the centerline of First Avenue, approaching Union Street. Crews will continue mining beneath First Avenue for several blocks. Then, at Stewart Street, where First Avenue veers to the west, tunneling crews will continue mining north en route to the spot near Seattle Center where Bertha will emerge.

As we’ve highlighted before (links to YouTube), the program has an extensive network of instruments in place to monitor ground movement. Crews continue to see little to no movement as they tunnel through a mixture of clay, sand and gravel beneath downtown.

The entire tunnel route, including descriptions of each of the 10 zones through which Bertha is mining, can be found on our Follow Bertha page. Tunneling statistics are updated on that page on Mondays and Thursdays. You can also track Bertha’s progress on Twitter @BerthaDigsSR99.

A look at the SR 99 tunnel as it curves toward First Avenue. Other recent project photos can be seen here.